Igniting device for a rocket, and its mounting thereon and manufacture

ABSTRACT

An igniter device comprises a ring containing a primary charge, and extending from the ring parallel to the axis thereof are hollow casings each containing a main charge. The main charge in each casing is operatively coupled to the primary charge through an orifice in the ring and a flame tube contiguous with the main charge. The igniter device can be mounted on a solid propellant rocket having a propellant unit with a set of arms separated by cavities into which the igniter casings are slidably engaged.

Mane et al.

1. 1 I 3,757,692 51 Sept. 11, 1973 IGNITING DEVICE FOR A ROCKET, AND

ITS MOUNTING THEREON AND MANUFACTURE [75] Inventors: Bertrand Yves Iliffolyte Maue;

Grebert Robert Emmanuel Omer, both of St. Medard en Jalles, France [73] Assignee: Etat Francais Represente par Le Ministre charge de La Defense Nationale, Paris, France 221 Filed: Apr. 23, 1971 21 Appl.No.: 136,874

[30] Foreign Application Priority Data Apr. 24, I970 France 70l5003 [52] US. Cl. I02/49.7, 60/256 [51] Int. Cl I42b 3/08 [58] Field of Search l02/49.7, 70; 60/256 [56] References Cited UNITED STATES PATENTS 3,581,662 6/l97l Cirebert 102/70 R 3,244,102 4/1966 Woffard et al. [02/24 HC 3,173,370 3/1965 Landry 102/70 R Primary Examiner-Benjamin A. Bor chelt Assistant ExaminerJ. V. Doramus Attorney-Waters, Roditi, Schwartz & Nissen [57] ABSTRACT An igniter device comprises a ring containing a primary charge, and extending from the ring parallel to the axis thereof are hollow casings each containing a main charge. The main charge in each casing is operatively coupled to the primary charge through an orifice in the ring and a flame tube contiguous with the main charge. The igniter device can be mounted on a solid propellant rocket having a propellant unit with a set of arms separated by cavities into which the igniter casings are slidably engaged.

5 Claims, 6 Drawing Figures Patented Sept. 11, 1973 3,757,692

3 Sheets-Sheet 1 Patented Sept. 11, 1973 3 SheetsSheet 2 Patented Sept. 11, 1973 s Sheets-Sheet is FIG 5 IGNITING DEVICE FOR A ROCKET, AND ITS MOUNTING THEREON AND MANUFACTURE BRIEF SUMMARY OF THE INVENTION The present invention relates to an igniting device, applicable for use with solid-propellant rockets and to its method of manufacture.

In rocketry, it is known to utilize igniters located fore and aft of the propellant unit, which igniters are most frequently composed of a tubular ring containing black powder or ignition pellets and serve for igniting the solid propellant units in the event the central portion of said units is not utilizable. I

Such igniting devices do not generally give particularly satisfactory results. Indeed, when such an igniter is secured to a metal portion of the rocket, it changes its location with respect to the propellant unit with variations in temperature (by reason of the different coefficients of expansion) or during the operations of loading into the casing. When the igniting device is secured by cementing on the propellant unit, it is subjected to strains on changes in temperature, which introduces problems as to the method of effectively starting the firing operation and impairing safety in operation due to the danger of separation between the various parts. The performance of such igniters where the firing charge is loose is not reproducible.

The igniter device according to this invention is intended to correct these drawbacks by allowing control of the ignition phenomenon.

According to the invention, the igniting device comprises a ring containing the primary charge and provided with hollow casings extending substantially parallel to the axis of the ring, each casing containing a main charge operatively connected to the primary charge.

The main charges can thus be fired by the primary charges to produce a set of appreciably parallel flame jets.

The primary charge is contained in a cord encased in the ring and the primary charge communicates with the casings through orifices in the ring.

According to a preferable embodiment of the invention, the casings contain a stack of ignition pellets forming the main charge, such stack being contiguous to a flame tube which communicates with the ring containing the primary charge.

According to the preferred embodiment of the invention, the igniting device is made of a flexible plastic material whose physical properties change only very slightly over a temperature range from -60C. to +70C. and which has a Shore hardness of approximately 60 and good tearing strength. Such plastic material may be a silicone rubber or a polyurethane rubber. These materials provide the igniting device with valuable mechanical properties favoring reproducibility of the results.

The invention also contemplates application of the igniting device of the type thus defined to a solidpropellant vehicle or rocket, in which application the rocket contains a solid propellant unit which comprises a plurality of spidered arms separated by cavities, the igniting device being mounted in relation to the propellant unit such that its casings enter the cavities provided between the arms of the propellant unit.

According to a preferred embodiment of the aforesaid application, the casings of the igniting device are slide-mounted in the cavities between the arms of the propellant unit.

Because of the respective arrangement of the propellant unit and its igniting device which permits their relative sliding motion while at the same time keeping the primary charge in close proximity to the propellant unit, the dangers of separation arising, for example, from expansion due to changes in temperature are voided. This promotes the reproducibility and uniformity of the ignition.

According to a favorable embodiment of the invention, the number of casings is less than the number of cavities.

It is preferable to arrange certain arms of the propellant unit into contact with a wall (such as the wall of an axial nozzle in the rocket) in order to produce a throttling of the gases at such wall at the time of firing.

Also according to the invention, the manufacture of the housing of the igniter device is effected by forming a core mold of material having a low melting temperature (of the order of 80C.), then molding the plastic of the igniting device around said core, and after polymerization of said plastic is completed, the aforesaid core is melted.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a longitudinal sectional view of the igniter device according to the invention, taken along line I-I of FIG. 2,

FIG. 2 is a plan view of the igniter device of FIG. 1,

FIG. 3 is a cross-sectional view-taken along line III- -III of FIG. 1,

FIG. 4 is an elevational view of a rocket element carrying the igniter device of the invention, the top portion being seen in longitudinal section along line IV--lV of FIG. 5,

FIG. 5 is a cross-sectional view taken along line VV of FIG. 4, and

FIG. 6 is a partial axial-section on a much larger scale of the mounting of the igniter device.

DETAILED DESCRIPTION Referring to FIG. 1 of the drawing, therein is seen an igniter which comprises a ring I supporting a plurality of hollow casings 5 extending parallel to axis AA of the hoop. The ring 1 and casings 5 are preferably made of a molded flexible plastic material whose physical characteristics vary but slightly over a temperature range from -60C. to +C. so as to offer approximately the same mechanical properties over such temperature interval. For this purpose a silicone rubber or polyurethane-base elastomer with a Shore hardness of 60 is satisfactorily used.

In the ring 1 is a primary charge 2 (also of annular form) and the charge 2 is encased in the ring 1. The charge 2 is composed of a powder mixture such as black powder or any other similar composition. Charge 2 is contained in a flexible tube 3. The cord thus fonned is inserted into an annular channel provided for that purpose in ring 1. The ring 1 is provided with a recess 4 adapted for containing the firing device of primary charge 2 or for initiating such firing. This firing device can be constituted by a relay unit which is actuated by a conventional electric igniter. Alternatively, an exploded wire initiator independent of the igniter can be used or any other standard electrical or pyrotechnical system. One example of such device is shown in FIG. 6.

The casings of the igniting device, can be present in any number suitable for the intended application of the igniter. In the illustrated embodiment, four casings are shown and these are integral with ring 1. Each casing 5 has a longitudinal cavity forming a flame tube 6. Through an orifice 7 made in ring 1 and opening into the primary charge 2, each flame tube 6 connects primary charge 2 with a main charge 8 which is formed by a stack of ignition pellets. The ignition pellets are housed in a longitudinal chamber 11 extending parallel to tube 6 and provided with bores 9 which connect chamber 11 with flame tube 6 on the one hand and with the outside on the other.

Preferably the plastic body of the igniting device is produced by the following method of manufacture:

A core of a substance fusible at low temperature, such as an alloy whose melting point is approximately 80C., is fabricated to reproduce all the hollow portions of the igniting device. The plastic material of the igniting device is then molded around the core and its polymerization completed. The device is then heated at a temperature above 80C. to melt the core material away. This is a simple and inexpensive process.

In the practice, the igniting device illustrated in FIGS. 1 and 2 is intended for use in conjunction with solid propellant units provided with cavities into which the casings 5 are introduced. One embodiment of such arrangement will be described hereafter.

The operation of the igniting device is as follows: the primary charge 2 is detonated by the igniter means provided, and the flames produced travel into the flame tubes 6 through the orifices 7 and then travel through the radial bores 9 into the chambers 11 which contain the main charge 8. This charge then ignites and the resulting flames pass through the bores 9 which open to the outside of casings 5 and make contact with the solid propellant which in turn is ignited.

ment will now be described of the igniting device for a rocket 21, partially shown, comprising an axial nozzle 22 and an annular propellant 23 arranged around the nozzle 22. Propellant 23 is housed in a jacket 24 provided with nozzles 25 distributed around nozzle 22 and forming nozzles for starting or accelerating rockets 21.

The nozzle 22 and jacket 24 are made of a material capable of withstanding extremely high temperatures.

According to the invention, the propellant 23 comprises a set of radial arms, some of which are short 26 and others long 27 (FIG. 5) distributed in annular array around the axis B-B of nozzle 22 and extending theretowards. Between the end portions of the arms 26 and 27 are formed longitudinal cavities 28 into some of which are introduced casings 5 of the igniting device of the type described, the ring 1 of said device resting on the top surface 29 of propellant 23. The igniting device is thus slide-mounted in propellant 23 and is preferably fastened in such a way that its sliding motion can be re-.

tained during the operation of the rocket. Thus in the embodiment of FIG. 6, ring 1 is attached to an annular plate 31 located inside a dish 32 and slide-mounted on studs 33 carried by a plate 34 attached to the propellant 23. Springs 35 are arranged around the studs 33 to urge plate 31 to an upper stop position while allowing sliding motion parallel to axis B-B under the action of accelerations and/or thermal effects.

According to one of the features of the invention, the number of casings 5 of the igniting device is less than the number of cavities 28, so that some of these cavities are unoccupied. Further, the long arms 27 of the propellant 23 are arranged to come into approximate contact with the outside wall of the nozzle 22. This approximate contact is understood to be a slight spaced relation or a slight contact between opposite surfaces of nozzle 22 and arms 27 as shown in FIG. 5, so as to produce in either case a throttling action against passage of combustion gases, whose transmission from the cavities 28 containing the casings 5 to the vacant cavities 28 is thus delayed.

In the embodiment of FIG. 6, there is further seen a relay unit 36 with priming electrodes 37, which is lodged in a duct 38 of base 39 of the rocket 21 to effect the firing of the igniter. Duct 38 communicates by a bore 41 with recess 4 which is left free to allow propagation of the flames.

The features and advantages of the device thus provided are as follows:

The relative motion allowed between casings 5 and arms 26, 27 of propellant 23, while keeping these elements appreciably in contact, results in said relative motion having only a negligible action on the rise-inpressure phase, thus assuring good reproducibility thereof and so increasing the reliability of the device.

Further, the structure of casings 5 allows a simultaneous ignition of specially determined portions of propellant 23. The ignition phenomenon can thus be controlled, which in the case of units offering a considerable self-locking action, allows elimination of a large portion of the pressure peak due to slow combustion of this unit, while guaranteeing safety in operation. Moreover, since the propellant 23 can be ignited at only a few points, the internal space occupied prevents instantaneous transmission of the ignition, thus also helping to produce a more gradual rise in pressure. Consequently, by manipulating the number and arrangement of the main charges (simultaneously detonated elementary igniters), for a unit of given section, the rise in pressure can be modified within certain limits for the desired direction.

The magnitude of slow combustion results, in the case of a conventional igniter, to a recessing or checkering at the back of the propellant, which changes the ballistic performance because of the actual mass of powder removed at the time of machining. The igniting device according to this invention allows that operation to be dispensed with.

Finally it will be noted that the use of a molded flexible material allows the igniting device to be very easily adapted firstly to the various forms of propellant that may be considered and secondly, the behavior of these materials to mechanical and thermal strains allows them to respond to the conditions currently involved in the ignition of propellant units. Furthermore, in the eventuality of destruction, the igniter does not endanger the nozzle.

The ignition reproducibility obtainable through this invention has been especially confirmed by the following tests corresponding to five firings performed inside a totally enclosed housing, the pressure being read inside the housing 1.

In the testing, the following designations are utilized:

d time allowed for ignition of the propellant;

D time elapsing from firing until reaching maximum pressure P;

D time interval from reaching pressure PM to reaching pressure 3P/4;

P value of maximum pressure The time periods are measured in milliseconds and the pressures in relative bars.

lgniter No. D D D P l 7.5 I005 34.5 14.05 2 6.2 99.5 33.4 12.7 3 7.0 l23.5 38 I09 4 7.2 99 35 ll.l 5 6.0 I23 34 10.3

Dia. of Weight Type of nozzles of Maximum Pressure igniter in mm powder on ignition (kg.) (relative bars) I Z X 70.4 100.350 l5 [.2 ll 2 X 70.4 97.870 l07 Ill 2 X 71.5 102.820 99.9

Igniter ll had six casings uniformly distributed in the cavities provided between the arms of the propellant. Because of the relative arrangement of the propellant and the igniter there is ignition reproducibility (unconstrained sliding motion of igniter inside the unit cavity). The reduction of the pressure peak due to the slow combustion phenomenon is obtained by means of a slight checkering made at the back of the propellant unit. The maximum pressure on ignition is 107 relative bars.

Igniter [II had four casings distributed in four cavities out of six(i.e., ignition of two-thirds of the propellant surface). Delayed ignition phenomenon is produced in the propellant unit. The actual presence of the internal occupation of the nozzle prevents instantaneous transmission of the ignition into the propellent mass (throttling of the gases against the external wall of the nozzle occupying the axial portion of the propellant unit). Beside reproducibility, the device offers the advantage of gradualness of ignition. It allows the initial overpressure to be reduced to the neighborhood of 99 relative bars (99.9 in the present case) without need to resort to a checkering operation which alters the ballistic performance by the weight of propellant removed. The igniter according to the invention thus offers the following additional advantages:

Propellant weight gain: 102.820 kg against 97.870 k and 100.350 kg (1) Reduction of residual and unburned portions, which confirms the structural lightness and efficiency of the propellant systems obtained. Further, the mechanical and thermal strains to which the propellant unit is subjected are correlatively reduced.

As to the conventional igniter of the hoop type I, its propellant mass is l00.350 kg, but the maximum pressure on ignition is high, namely 151.2 relative bars, which means an extremely troublesome internal pressure peak because of the simultaneous ignition, given the large internal surface area and the low free volume, which is reduced by reason of the internal filling.

It is clear that the igniter device according to the invention can be varied and modified relative to the embodiments described, without exceeding the scope of the invention. Thus, the shape and volume of the easings 5 can be changed, especially correlative with the shape of the cavities in the propellant unit.

What is claimed is:

1. An igniter device comprising a ring containing a primary charge, said ring being provided with orifices, hollowcasings on said ring extending substantially parallel to the axis of the ring, said casings comprising respective longitudinal cavities forming respective flame tubes extending parallel to said axis and communicating with said primary charge through said orifices, and respective longitudinal chambers extending parallel to said cavities and contiguous therewith, said chambers having peripherical apertures, and respective main charges in said, chambers operatively connected with said primary charge respectively through said flame tubes respectively contiguous with said chambers.

2. An igniter device as claimed in claim 1, comprising respective stocks of pellets in said chambers respectively forming said respective main charges.

3. An igniter device as claimed in claim 1, wherein said ring and casings are constructed of a flexible plastic material whose physical properties are substantially constant over a temperature interval from 60C. to +C.

4. An igniter device as claimed in claim 3, wherein said flexible plastic material has a Shore hardness of approximately 60.

5. An igniter device as claimed in claim 3, wherein said flexible plastic material is an elastomer of silicone rubber or polyurethane rubber.

1! II t i t 

1. An igniter device comprising a ring containing a primary charge, said ring being provided with orifices, hollow casings on said ring extending substantially parallel to the axis of the ring, said casings comprising respective longitudinal cavities forming respective flame tubes extending parallel to said axis and communicating with said primary charge through said orifices, and respective longitudinal chambers extending parallel to said cavities and contiguous therewith, said chambers having peripherical apertures, and respective main charges in said, chambers operatively connected with said primary charge respectively through said flame tubes respectively contiguous with said chambers.
 2. An igniter device as claimed in claim 1, comprising respective stocks of pellets in said chambers respectively forming said respective main charges.
 3. An igniter device as claimed in claim 1, wherein said ring and casings are constructed of a flexible plastic material whose physical properties are substantially constant over a temperature interval from -60*C. to +70*C.
 4. An igniter device as claimed in claim 3, wherein said flexible plastic material has a Shore hardness of approximately
 60. 5. An igniter device as claimed in claim 3, wherein said flexible plastic material is an elastomer of silicone rubber or polyurethane rubber. 